California is nearly impossible. And non-stops to IST are harder to find than connecting flights, due to the married segment logic used by TK.

Try SEA, IAH, IAD, ORD and DET.

Keep in mind that M&S is not like other FFPs, where it is relatively easy to call up later and add a segment. You essentially must have award availability for your entire itinerary at the time you add TBS. If you are definitely going all the way through to TBS, you'd be wasting your time by trying to "hold" a USA-IST award until IST-TBS opens for booking...